我会做
type
TRestrictedString = record
strict private type
TBounds = record
MinLength,
MaxLength: integer;
end;
strict private
FStr: string;
public
Bounds: TBounds;
procedure SetString(const AString: string);
function GetString: string;
constructor Create(AMinLength, AMaxLength: integer); overload;
constructor Create(AMinLength, AMaxLength: integer; const AString: string); overload;
constructor Create(const AString: string); overload;
class operator Implicit(S: string): TRestrictedString;
class operator Implicit(S: TRestrictedString): string;
class operator Equal(const A, B: TRestrictedString): boolean;
class operator NotEqual(const A, B: TRestrictedString): boolean;
class operator Add(const A, B: TRestrictedString): TRestrictedString;
end;
{ TRestrictedString }
constructor TRestrictedString.Create(AMinLength, AMaxLength: integer);
begin
Bounds.MinLength := AMinLength;
Bounds.MaxLength := AMaxLength;
FStr := '';
end;
constructor TRestrictedString.Create(AMinLength, AMaxLength: integer;
const AString: string);
begin
Bounds.MinLength := AMinLength;
Bounds.MaxLength := AMaxLength;
SetString(AString);
end;
class operator TRestrictedString.Add(const A,
B: TRestrictedString): TRestrictedString;
begin
result.Bounds := A.Bounds;
result.SetString(A.GetString + B.GetString);
end;
constructor TRestrictedString.Create(const AString: string);
begin
Bounds.MinLength := 0;
Bounds.MaxLength := MaxInt;
FStr := AString;
end;
class operator TRestrictedString.Equal(const A, B: TRestrictedString): boolean;
begin
result := A.GetString = B.GetString;
end;
function TRestrictedString.GetString: string;
begin
result := FStr;
end;
class operator TRestrictedString.Implicit(S: TRestrictedString): string;
begin
result := S.GetString;
end;
class operator TRestrictedString.NotEqual(const A,
B: TRestrictedString): boolean;
begin
result := A.GetString <> B.GetString;
end;
class operator TRestrictedString.Implicit(S: string): TRestrictedString;
begin
result.Create(S);
end;
procedure TRestrictedString.SetString(const AString: string);
begin
with Bounds do
if (length(AString) < MinLength) or (length(AString) > MaxLength) then
raise Exception.Create('Invalid length of string.');
FStr := AString;
end;
现在你可以做很自然的事情了,比如
procedure TForm1.Button1Click(Sender: TObject);
var
str: TRestrictedString;
begin
str.Create(5, 10); // Create a string w/ length 5 to 10 chrs
str.SetString('Testing!'); // Assign a compatible string
ShowMessage(str); // Display the string
end;
你也可以这样做
str.Create(5, 10, 'Testing!');
ShowMessage(str);
您可以按通常的方式添加字符串:
var
s1, s2, s3: TRestrictedString;
begin
s1.Create(2, 10, 'Hi ');
s2.Create(2, 10, 'there!');
s3 := s1 + s2;
ShowMessage(s3);
end;
甚至
var
s1, s3: TRestrictedString;
begin
s1.Create(2, 10, 'Hi ');
s3 := s1 + 'there!';
ShowMessage(s3);
当您添加两个TRestrictedString
s 或一个TRestrictedString
和 astring
时,结果将具有与第一个操作数相同的限制。你可以试试
var
str: TRestrictedString;
begin
str.Create(5, 10);
str.SetString('Testing!');
str := str + '!!';
ShowMessage(str);
这会起作用,但不是
var
str: TRestrictedString;
begin
str.Create(5, 10);
str.SetString('Testing!');
str := str + '!!!';
ShowMessage(str);
请注意,将a分配string
给 aTRestrictedString
也会分配字符串的“边界”,也就是说,TRestrictedString
将边界设置为0
and MaxInt
。因此,无论 a 受到怎样的s: TRestrictedString
限制,分配s := 'some string'
总是有效的。
更新: Chris Rolliston 将此答案用作一篇非常有趣的文章的灵感。